Design and development of a small-scale cement-based 3D printing robot extrusion nozzle

Additive manufacturing (AM), also known as three-dimensional (3D) printing, offers great potential to create complex structures layer by layer from computer-aided design (CAD) models. Despite advancements in printable concrete technology, controlling printing quality remains a challenge associated with both the geometric and materials design of the printer nozzle, especially for small-scale printing that may be required by small and medium-sized enterprises (SMEs). Therefore, this study explored the design and development of a robot nozzle system, optimised for a small-scale 3D printing of cement-based structures. Key design considerations included weight, nozzle diameter/shape, material compatibility, flow control, mixing mechanism, temperature resistance, cost-effectiveness, adaptability, safety, and ease of maintenance. Iterative designs were developed, focusing on stress concentration mitigation and material flow optimisation. The challenge of incorporating mixing mechanisms during nozzle designs was discussed, leading to the adoption of an on-demand accelerator spraying system. This method involved a micro-peristaltic pump connected to an accelerator tank, spraying accelerator onto the surface of the deposited material, as the robot moved along its programmed path. Evidently, both the nozzle design and the spraying approach improved the buildability and print quality of the extrusion-based 3D-printed cement-based structures.